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chen Shang wrote:
>I minimized my patch and against to 2.6.12-rc4 this time, see below.
>
>The new schedstat fields are for the test propose only, so I removed
>them completedly from patch. Theoritically, requeue_task() is always
>cheaper than dequeue_task() followed by enqueue_task(). So, if 99% of
>priority recalculation trigger requeue_task(), it will save.
>
>In addition, my load is to build the kernel, which took around 30
>minutes with around 30% CPU usage on 2x2 processors (duel processors
>with HT enable).
>Here is the statistics:
>
>CPU0: priority_changed (669 times), priority_unchanged(335,138 times)
>CPU1: priority_changed (784 times), priority_unchanged(342,419 times)
>CPU2: priority_changed (782 times), priority_unchanged(283,494 times)
>CPU3: priority_changed (872 times), priority_unchanged(365,865 times)
>
>
OK that gives you a good grounds to look at the patch, but _performance_
improvement is what is needed to get it included.
>Thanks,
>-chen
>
>
>/*=====Patch=====*/
>--- linux-2.6.12-rc4.orig/kernel/sched.c 2005-05-19 14:57:55.000000000 -0700
>+++ linux-2.6.12-rc4/kernel/sched.c 2005-05-19 23:47:22.000000000 -0700
>@@ -2613,7 +2613,7 @@
> struct list_head *queue;
> unsigned long long now;
> unsigned long run_time;
>- int cpu, idx;
>+ int cpu, idx, prio;
>
> /*
> * Test if we are atomic. Since do_exit() needs to call into
>@@ -2735,9 +2735,17 @@
> delta = delta * (ON_RUNQUEUE_WEIGHT * 128 / 100) / 128;
>
> array = next->array;
>- dequeue_task(next, array);
>+ prio = next->prio;
>+
> recalc_task_prio(next, next->timestamp + delta);
>- enqueue_task(next, array);
>+
>+ if (unlikely(prio != next->prio))
>+ {
>+ dequeue_task(next, array);
>+ enqueue_task(next, array);
>+ }
>+ else
>+ requeue_task(next, array);
>
Coding style says
if (unlikely()) {
...
} else
...
-
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